On the origin of ultra high energy cosmic rays: Subluminal and superluminal relativistic shocks

Abstract

The flux of Ultra High Energy Cosmic Rays (UHECRs) at $E>10^{18.5}$ eV is believed to arise in plasma shock environments in extragalactic sources. In this paper, we present a systematic study of particle acceleration by relativistic shocks, in particular concerning the dependence on bulk Lorentz factor and the angle between the magnetic field and the shockflow. For the first time, simulation results of super- and subluminal shocks with boost factors up to $\Gamma =1000$ are investigated and compared systematically. While superluminal shocks are shown to be inefficient at the highest energies ($E>10^{18.5}$ eV), subluminal shocks may provide particles up to $10^{21}$ eV, limited only by the Hillas-criterion. For the subluminal case, we find that mildly relativistic shocks, thought to occur in jets of Active Galactic Nuclei (AGN, $\Gamma \sim 10-30$) yield energy spectra of $dN/dE\sim E^{-2}$. Highly relativistic shocks expected in Gamma Ray Bursts (GRBs, $100<\Gamma <1000$), on the other hand, have spectra as flat as $E^{-1.5}$. The model results are compared to the measured flux of Cosmic Rays at the highest energies and it is shown that, while AGN spectra are well-suited, GRB spectra are too flat to explain the observed flux. The first evidence of a correlation between the Cosmic Ray flux above $5.7\cdot 10^{10}$ GeV and the distribution of AGN by Auger are explained by the model. Neutrino production is expected in GRBs, either in mildly or highly relativistic shocks and although these sources are excluded as the principle origin of UHECRs, superluminal shocks in particular may be observable via neutrino and photon fluxes, rather than as protons.

arXiv comment38 pages, 9 figures, 2 tables submitted in a revised form in Astron.& Astroph

References in corpus (31)

• Gamma-Ray Bursts and the Fireball Model
• High Energy Neutrinos from Cosmological Gamma-Ray Burst Fireballs
• High Energy Neutrinos from Astrophysical Sources: An Upper Bound
• EGRET Observations of the Extragalactic Gamma Ray Emission
• Luminosity-dependent evolution of soft X-ray selected AGN: New Chandra and XMM-Newton surveys
• KASCADE measurements of energy spectra for elemental groups of cosmic rays: Results and open problems
• On the acceleration of Ultra High Energy Cosmic Rays in Gamma Ray Bursts
• High-energy Neutrino Astronomy: The Cosmic Ray Connection
• Particle acceleration at ultrarelativistic shocks: an eigenfunction method
• On the cosmic ray bound for models of extragalactic neutrino production
• High-energy neutrinos in the context of multimessenger physics
• Energy spectra of cosmic rays accelerated at ultrarelativistic shock waves
• Neutrinos From Individual Gamma-Ray Bursts in the BATSE Catalog
• High Energy Neutrino Emission and Neutrino Background from Gamma-Ray Bursts in the Internal Shock Model
• Monocular Measurement of the Spectrum of UHE Cosmic Rays by the FADC Detector of the HiRes Experiment
• A Note on High Energy Neutrinos from AGN Cores
• Multi-year search for a diffuse flux of muon neutrinos with AMANDA-II
• Diffusive Shock Acceleration in Unmodified Relativistic, Oblique Shocks
• Neutrinos as a diagnostic of cosmic ray Galactic/extra-galactic transition
• Comment on the first-order Fermi acceleration at ultra-relativistic shocks
• A Composite Seyfert 2 X-ray Spectrum: Implications for the Origin of the Cosmic X-ray Background
• A method of estimation of the dynamical age of FR II-type radio sources from multifrequency data
• On the generation of UHECRs in GRBs: a reappraisal
• The diffuse neutrino flux from FR-II radio galaxies and blazars: A source property based estimate
• Coincident GRB neutrino flux predictions: Implications for experimental UHE neutrino physics
• Particle acceleration in ultra-relativistic oblique shock waves
• The Cosmic Ray Proton Spectrum determined with the Imaging Atmospheric Cherenkov-Technique
• Numerical Integration of Nonlinear Wave Equations for General Relativity
• Two-dimensional PIC simulations of ion-beam instabilities in Supernova-driven plasma flows
• Particle acceleration in ultra-relativistic parallel shock waves
• Collisionless Dissipative Nonlinear Alfven Waves: Nonlinear Steepening, Compressible Turbulence, and Particle Trapping

Cited by in corpus (16)

• High-energy neutrinos from radio galaxies
• Monte Carlo Simulations of Nonlinear Particle Acceleration in Parallel Trans-relativistic Shocks
• Time-Dependent Searches for Point Sources of Neutrinos with the 40-String and 22-String Configurations of IceCube
• Neutrinos from active black holes, sources of ultra high energy cosmic rays
• Low-frequency study of two giant radio galaxies: 3C35 and 3C223
• Muon Acceleration in Cosmic-ray Sources
• Prediction of the diffuse neutrino flux from cosmic ray interactions near Supernova Remnants
• Active Galactic Nuclei Jets and Multiple Oblique Shock Acceleration: Starved Spectra
• Searches for high-energy neutrino emission in the Galaxy with the combined IceCube-AMANDA detector
• Ultra-High-Energy Cosmic Rays from Low-Luminosity Active Galactic Nuclei
• Limits on the source properties of FR-I galaxies from high-energy neutrino and gamma observations
• IceCube expectations for two high-energy neutrino production models at active galactic nuclei
• Neutrinos from photo-hadronic interactions in Pks2155-304
• Photon and neutrino emission from active galactic nuclei
• Photohadronic Modelling of the 2010 Gamma-ray Flare from Mrk 421
• Cosmic ray transport and anisotropies to high energies